1. Field of the Invention
The present invention relates in general to fluid actuated systems and particularly concerns a plurality of fluid pressure distribution networks arranged in fluidic parallelism to increase system reliability.
2. Description of Prior Developments
Fluid pressure distribution systems have been developed to supply a different fluid pressure and flow to each of several lines from a common source. These systems are capable of rapidly changing the pressure and flow in any selected line through a computer controlled valving arrangement known as a fluidic multiplexer. An example of such a system is disclosed in pending U.S. patent application Ser. No. 156,688 filed Feb. 17, 1988, and assigned to the Assignee of the present application, the entire specification of which is incorporated herein by reference.
Although fluidic multiplexers perform well for their intended purposes, such devices may present a reliability concern when controlled or operated under dual or redundant electronic control systems. That is, even though fluid-mechanical systems are generally considered less likely to fail than their associated electronic controls, recent developments in electronic controls have resulted in dual, or triple redundant electronic control systems. These redundant control systems provide very good electrical and electronic reliability which is far better than that of non-redundant control systems.
More particularly, should one electronic control system fail, a second control system automatically provides the required control signals to maintain the fluid-mechanical system in operation. However, should the single fluid-mechanical system fail, no back up is available with existing designs so that the single fluid-mechanical system now becomes the most likely source of failure. As fluidic multiplexers may be adapted for use in operating, for example, a gas turbine engine in an aircraft, reliability of the fluid-mechanical system and its associated electronic controls becomes a critical concern.
Multiplexers permit the control of a plurality of actuators from a single electronic control source. In an aircraft engine, one multiplexer can be utilized to operate several actuators. By way of an example, it can be used to simultaneously operate the actuator which opens and closes a bleed door for bleeding the pressurized air from a booster stage of the engine, for operating the actuators which control the engine variable stator vanes, thereby controlling the angle of attack of the compressor blades on the engine, for controlling the fuel valve which controls the amount of fuel delivered to combusters, and for thrust reversing and thrust vectoring systems. The actuators are generally in the form of pistons whose stroke is controlled by means of the hydraulic servo control system. It is foreseeable, that as gas turbine technology advances, and even greater numbers of hydraulic actuators will come into use.
As greater needs for actuators are defined, it becomes more practical to group the actuators for control by a single multiplexer. Accordingly, a need exists for a fluid mechanical system which provides a degree of reliability which matches or exceeds that of any associated dual or redundant electronic controls used to actuate the fluid-mechanical system. This is particularly the case with fluidic multiplexers used in aircraft gas turbine engines where dual or redundant electronic control systems are presently used to control a single or non-redundant fluid-mechanical or hydromechanical actuation system.